This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-368691, filed Dec. 4, 2000, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a polarized light reflecting element, a liquid crystal display element including the polarized light reflecting element, and a method of manufacturing the polarized light reflecting element.
2. Description of the Related Art
It is generally known that a cholesteric or chiral-nematic liquid crystal film that has a helical molecule array and a helical axis extending substantially in the normal direction exhibits circular-polarization dichromatism. The term xe2x80x9ccircular-polarization dichromatismxe2x80x9d means the character of the film that reflects those circularly polarized light components of incident light which have a specific wavelength and a specific direction and transmits circularly polarized light components in a direction opposite to the direction of the reflected light components.
The reflection and transmission characteristics for the circular-polarization dichromatism are settled depending on the helical structure of the liquid crystal used. Thus, the direction of the circularly polarized light to be reflected is coincident with the direction of helixes of the liquid crystal, and its wavelength depends on the pitch of the helixes. Further, the reflectance and transmittance change according to the thickness of the liquid crystal film. The thicker the film, the higher the reflectance is.
Polarized light reflecting elements with various polarized light reflection characteristics can be obtained by controlling the direction and pitch of the helixes of the liquid crystal film and the film thickness, taking advantage of the aforesaid characters. The polarized light reflecting elements can be applied to transmission- or half-transmission-type liquid crystal display elements that utilize circularly polarized light for display, and serve as useful luminance improving films for improving the utilization factor of a light source.
The degree of circular polarization of reflected and transmitted light is essential to the polarized light reflecting elements used for this purpose. Thus, if circularly polarized light in a direction opposite to a desired direction is mixed in the reflected and transmitted light, the resulting leakage light lowers the functions of the polarized light reflecting elements.
In the conventional polarized light reflecting elements, however, the degree of circular polarization of reflected and transmitted light is not high enough. If one such polarized light reflecting element is applied to a liquid crystal display element, therefore, leakage light increases to lower the contrast, so that the quality level of display of the display element lowers. If the reflecting element is used as a luminance improving film, moreover, the light utilization factor lowers inevitably. Thus, the function of the polarized light reflecting element cannot be used efficiently.
The present invention has been contrived in consideration of these circumstances, and its object is to provide a polarized light reflecting element for improving the degree of circular polarization of reflected and transmitted light, thereby ensuring a high light utilization factor, a liquid crystal display element using the polarized light reflecting element, and a manufacturing method for the polarized light reflecting element.
In order to achieve the above object, a polarized light reflecting element according to an aspect of the present invention comprises at least one polymerized liquid crystal layer, cholesteric, chiral-nematic, or chiral, having a helical liquid crystal molecule array and a helical axis extending substantially in the normal direction, the in-plane mean value xcex1 of the respective helix angles of the liquid crystal molecules being given by
nxcfx80xe2x88x920.05xcfx80xe2x89xa6xcex1xe2x89xa6nxcfx80+0.05xcfx80 (n=1, 2, 3, . . . ). 
According to the polarized light reflecting element constructed in this manner, the degree of circular polarization of reflected and transmitted light can be drastically improved to ensure a high light utilization factor.
A half-transmission-type liquid crystal display element according to another aspect of the invention comprises a first polarization plate, a liquid crystal cell, a second polarization plate, and the polarized light reflecting element located between the first and second polarization plates.
Further, a liquid crystal display element according to still another aspect of the invention comprises a first polarization plate, a liquid crystal cell, a second polarization plate, a backlight source, the polarized light reflecting element located between the second polarization plate and the backlight source, and a xcex/4-wavelength plate located between the second polarization plate and the polarized light reflecting element.
According to the liquid crystal display element constructed in this manner, high-contrast display characteristics can be obtained with use of the polarized light reflecting element that enjoys the high light utilization factor.
A method of manufacturing a polarized light reflecting element according to a further aspect of the invention comprises a process for forming an oriented film on a substrate, a process for orienting the oriented film so that liquid crystal molecules are controlled in one in-plane direction, a process for forming a liquid crystal layer having a helical structure on the oriented film, and a process for orienting and solidifying the liquid crystal molecules in the top portion of the liquid crystal layer in substantially the same direction as the direction of orientation of the oriented film.
Further, a method of manufacturing a polarized light reflecting element according to another aspect of the invention comprises a process for forming a first oriented film on a substrate, a process for orienting the first oriented film so that liquid crystal molecules are controlled in one in-plane direction, a process for forming a first liquid crystal layer having a helical structure on the first oriented film, a process for orienting and solidifying the top portion of the first liquid crystal layer in substantially the same direction as the direction of orientation of the first oriented film, a process for forming a second oriented film on the first liquid crystal layer, a process for orienting the second oriented film in substantially the same direction as the direction of orientation of the first oriented film, a process for forming a second liquid crystal layer on the second oriented film, and a process for orienting and solidifying the top portion of the second liquid crystal layer in substantially the same direction as the direction of orientation of the first oriented film.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.